Field of the Invention
The present invention relates to a process and a device for manufacturing a honeycomb body, in particular a supporting body for catalytic converters in exhaust gas cleaning systems, as preferably fitted in motor vehicles.
The general construction of such honeycomb bodies is described, for example, in European Patent 0 454 712 B1, corresponding to U.S. Pat. No. 5,157,010. That document also describes so-called transversal microstructures, which are fitted for influencing the flow and improving the effectiveness of a catalytic converter. Honeycomb bodies are wound, laminated or layered or interlaced from at least partially structured metal sheets, wherein the structure of the metal sheets additionally results in the formation of channels through which an exhaust gas can pass. For that reason, the main structure determines the size of the channels. A microstructure is understood in the description given below, as in the prior art, to be a structure of substantially smaller dimensions than the main structure, wherein the microstructure should preferably be disposed at an angle or perpendicularly with respect to the direction of the channels in the honeycomb body. In order to manufacture a microstructure disposed in that way, it is necessary to structure a metal foil band along its longitudinal direction or at an angle with respect thereto. Considerable cold forming is necessary for such structuring, if it is to result in a continuous passage without a great degree of change in the width of the metal foil band.
Metal foils which are constructed from two or more layers and are intended for the manufacture of metallic honeycomb bodies, are known from European Patent 0 159 468 B1 and U.S. Pat. No. 5,366,139. Metal foils that are constructed in such a layered or laminated manner can be rolled from the desired alloy components, in which steel sheets roll-bonded with aluminum are preferably used. In principle it is possible to homogeneously anneal such foils after rolling, whereby a high-temperature corrosion resistant material, that is suitable in every way for the manufacture of metallic honeycomb bodies, is produced. However, that homogenous annealing is costly in terms of energy and increases the cost of the rolling process which in itself is very inexpensive.
It has also been proposed previously to manufacture honeycomb bodies from roll-bonded metal foils which have not yet been homogeneously annealed and to combine the homogeneous annealing with a brazing process that is in any case subsequently necessary. Although that variation is less expensive in terms of energy consumption, it requires that the steps which are necessary for the structuring of the metal sheets be carried out on a roll-bonded foil that is not heat-treated. It has, however, been shown that certain production steps, in particular the manufacture of microstructures, cannot be carried out without problems because of the poor capability of the roll-bonded material to be cold formed, since roll-bonded metal foils can be cold formed by no more than 1% without tearing.
Lastly, manufacturing methods for honeycomb bodies are also known in which not all of the honeycomb body is brazed at the end and thereby subjected to a heat treatment process. Thus, for example, honeycomb bodies such as are described in International Patent Application WO 89/07488 or other honeycomb bodies with involute or S-shaped metal sheets can also be joined together into a sturdy composite, in such a way that the ends can simply be welded or brazed onto a sheathed pipe, without the need to heat the metals foils in their entirety. With that manufacturing process, if the metal foils are neither homogeneously annealed or otherwise heat treated they lack a sufficiently thick oxide layer, which is desirable for the adhesion of a later catalytically active coating.